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Flashcards in Fluid and Renal Physiology Deck (143)
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What are the 2 largest compartments of ECF?

1. Interstitial Fluid
2. Plasma


What electrolytes are in ECF?

LOTS of Na and Chloride, small amount of Mg, K, P, Ca, organic acids


What electrolytes are in ICF?

Lots of K and phosphate, moderate amount of Mg, sulfate


What is osmolality?

Number of osmoles per kg of water


What is osmolarity?

Number of osmoles per liter of water


Causes of hyponatremia = hypoosmotic dehydration

Primary hyponatremia; Adrenal insufficiency - Addison's dz; overuse of diuretics


Causes of hyponatremia = hypoosmotic overhydration

Excess water diluting Na; Excess ADH (Syndrome of inapporpirate ADH) = Kidney absorbs more water


Causes of hypernatremia = hyperosmotic dehydration

Due to loss of water; Dehydration (most common); Inability to secrete ADH (Diabetes insipidus)


Causes of hypernatremia = hyperosmotic overhydration

Due to gain of Na; Excessive secretion of Na retaining hormone = Aldosterone


What happens with hyponatremia?

Hyponatremia = Cell Swelling → Osmotic mediated demyelination of neurons


What happens with hypernatremia?

Hyponatremia = Cell Shrinking → Stimulating thirst mechanism in hypothalamus


What are the 4 major causes of Extracellular Edema?

• Increased Capillary pressure (excessive kidney retention of salt and water, high venous pressure and venous constriction, decreased arteriole resistance)
• Decreased plasma proteins (Loss of proteins in urine, loss of proteins from denuded skin (burns), failure to produce proteins (liver failure))
• Increased capillary permeability (Immune rxn = histamine, toxins, bacterial infections, Vitamin def (esp Vit C), prolonged ischemia, burns)
• Blockage of Lymph Return (cancer, infections, sx, congenital/lymphatic abnormality)


What is intracellular edema?

Swelling in the cell itself; caused by hyponatremia, decreased cellular metabolic activity or nutrient delivery


What are the 4 safety factors that normally prevent edema?

o Low interstitial compliance: normal interstitial pressure is subatmospheric = low compliance; when interstitial fluid is present, this increase in interstitial hydrostatic pressure deters capillary filtration; when pressure is zero or positive, increased compliance occurs = more fluid contributes less to hydrostatic pressure = allows more water accumulation
o Interstitial gel: most water in the interstitium is in the form of a gel (bound to proteoglycans) = provides the low compliance at negative pressures; as the pressure increases and the increased compliance allows for more water accumulation, it becomes free (not bound to proteoglycans) = “pitting edema”; in edema, excess fluid forms channels through proteoglycans = fluid can flow to gravity-dependent regions
o Increased lymph flow: can increase 10-50 X normal
o Washdown of the interstitial fluid protein: as the interstitial fluid pressure increases, the lymph flow also increases and removes proteins at a more rapid pace.


Name 7 functions of the kidenys in homeostasis.

o Regulation of water and electrolyte balance
o Excretion of metabolic waste products (urea, creatinine, uric acid, bilirubin)
o Regulation of arterial blood pressure (via renin)
o Regulation of acid-base balance
o Produces 1,25 cholecalciferol (active VitD, calcitriol - Ca deposition in bone, Ca reabsoprtion in GIT)
o Produces EPO from the peritubular endothelial cells
o Glucose synthesis (rivals liver in some situations)


Why is the renal circulation unique?

Two capillary beds separated by efferent arteriole; afferent arterioles →glomerular capillaries →efferent arteriole →peritubular capillaries →venous system


How do the 2 capillary beds in the kidney work?

Glomerulus (high pressure) = Filtration
Peritubular caps (low pressure) = Reabsorption


How does the kideny regulate hydrostatic pressure?

By adjusting resistance in afferent and efferent arterioles - Kidney can regulate hydrostatic pressure in both capillary beds (glomerular and peritubular) to change the rate of glomerular filtration and tubular reabsorption, or both


Each nephron contains….

1. Glomerulus
2. Long tubule


Name the order to tubular segments of the nephron.

Glomerular capillaries surrounded by Bowman’s capsule = proximal tubule = Loop of Henle (descending thin, ascending thin, ascending thick) = distal tubule = cortical collecting tubule = cortical collecting ducts


What is the macula densa?

At end of the thick ascending limb; Plaque of specialized epithelial cells (aids in controlling nephron function)


What are the regional differences in nephron structure?

1. Cortical nephrons are located in the cortex and have short loops of Henle
• Have peritubular capillaries
2. Juxtamedullary nephrons are adjacent to the medulla and have long loops of Henle
• Have vasa recta which originate as efferent arterioles that form an extensive capillary network around the Loop of Henle, return to the cortex and enter into cortical veins


What is the name of the reflex that results in urine in bladder being propelled backwards?

Vesicoureteral Reflex


Name the 3 major nerves involved in bladder innveration and their function.

1. Pelvic nerve (PNS)
• Sensory fibers detect the degree of stretch
• Motor fibers facilitate detrusor contraction
2. Pudendal nerve (skeletal): innervates the external urethral sphincter
3. Hypogastric nerve (SNS, from L1-L4):
• B-adrenergic = detrusor relaxation
• A-adrenergic = internal urethral sphincter contraction


Describe the storage phase of micturition.

Storage phase: under SNS tone via hypogastric nerve
• b-adrenergic: detrusor relaxation
• α-adrenergic: contract IUS
• Somatic: contract external urethral sphincter


Describe the micturition reflex.

Micturition reflex = causes the transition from storage to voiding phase
• Afferent limb: stretch receptors in bladder wall → impulses via pelvic nerve → micturition center in brainstem → reach threshold for reflex
• Efferent limb: motor discharges to the sacral PNS nuclei initiate the voiding phase


Describe the voiding phase of micturition.

Voiding phase: under PNS tone via the pelvic nerve
• PNS stimulation → detrusor contraction
• Inhibition of SNS activity → relaxation of IUS
• Urine flow should be sustained until emptying is complete


Why is the glomerular capillary bed unique?

It has 3 membranes (instead of two)


What are the 3 layers of the glomerular capillary membrane?

1. Capillary endothelium: contains fenestrations, large enough to allow protein passage
2. Glomerular basement membrane: negatively charged proteoglycans that effectively prevent the passage of plasma proteins
3. Epithelial cells (podocytes) surrounding the outer layer of the basement membrane = contain slit-pores with some filtration restriction


What is the main barrier to filtration of plasma proteins in glomerulus?

Basement membrane